Heat transfer between a surface and an adjacent gas stream flowing substantially parallel thereto is affected by a variety of factors, including gas velocity, surface roughness, gas density, etc. It is known in the art to use roughening ribs or ridges disposed generally transversely with respect to the flow direction of the adjacent gas stream for the purpose of augmenting overall heat transfer coefficients and rates. Such roughening ribs may be disposed perpendicularly, skewed, or in chevrons as disclosed in U.S. Pat. No. 4,416,585 issued to Abdel-Messeh. Such configurations, while generally increasing overall heat transfer coefficient and hence rates, do not provide consistent or determinable augmentation of local heat transfer coefficient between the surface and the adjacent gas stream.
For certain applications, and in particular for internally cooled gas turbine airfoils exposed to an external stream of high temperature turbine working fluid, it is particularly desirable to minimize the flow of internal cooling gas through the turbine blade while still maintaining thermal protection at the external blade surface. As will be appreciated by those skilled in the art of turbine blade cooling, the heat loading at the exterior of the blade is not uniform with chordal displacement, having a peak at the leading edge of the blade and subsequent intermediate peaks at various locations disposed along the pressure and suction sides of each individual blade. Prior art heat transfer augmenting ribs are typically sized to achieve sufficient overall internal heat transfer rates so as to protect the high heat load zones of the blade, thereby overcooling other, lesser loaded zones.
A heat transfer augmenting configuration which permits the designer to allocate and vary heat transfer augmentation transversely with respect to the cooling gas flow would achieve protection of the blade exterior at reduced overall internal cooling mass flow.